Combustion cameras have been designed and used for the visualization of the combustion process in industrial gas turbines. The known design have utilized air to cool the camera used in the assembly, which generally is a charged-coupled device (“CCD”) camera. Because of the limitations associated with using air as a coolant, these assemblies were relatively large. Nevertheless, these assemblies were still not sufficiently cooled, which often caused the CCD camera to malfunction because of its sensitivity to heat. The larger size required by the air cooling medium necessitated approximately a 2.0-inch (about 5 cm) diameter opening in the combustion chamber to view the combustion process. An opening of this size, however, is generally larger than what is acceptable in commercial gas turbines.
Further, the known combustion cameras assemblies generally had been mounted on the outside of the gas turbine such that only a small portion of the camera, such as a lens set, extended into the high temperature and high pressure turbine environment. Mounting the combustion camera entirely inside the gas turbine, as now required by many commercial gas turbines, may greatly overheat the CCD camera and result in failure.
Known combustion cameras generally included as a design feature a threaded mechanical fastener and gasket arrangement to mount and seal the quartz window cap, which is the transparent layer through which the CCD camera views the combustion process. This arrangement, however, has two undesirable effects: (1) a large camera housing diameter and (2) frequent servicing of the gaskets due to deterioration in the high temperature environment.
Known combustion cameras also have included assemblies that have been adapted from camera designs used for viewing the combustion process in boilers. These adapted assemblies also were air-cooled and, as a result, were large in size. Another popular design included the separation of the lens from the camera. The lens of such camera assemblies generally included a “lens sets” that was used to project the combustion process image back to the CCD camera, which was located outside of the boiler. This arrangement allowed only the lens sets to be located in the extreme temperature and pressure conditions of the turbine. The drawbacks of this design include light attenuation and image distortion. Light attenuation prevents observation of low light aspects of the combustion process, such as observing the spark during the ignition process. Image distortion causes the image to be somewhat blurry, which prevents the observation of the fine details of the combustion process.
Many of the newer industrial gas turbines require that combustion camera assemblies be designed to satisfy the following criteria: (1) operate while installed entirely within a 350 psi, 825° F. (24.6 kg/cm2, 440° C.) environment and while viewing a 3000° F. (1650° C.) combustion process; (2) cooled in such a manner that the cooling medium is not exhausted into the combustor, which can affect the combustion process thus making it not representative of the actual process; (3) view the combustion process through a 1.0-inch (about 2.5 cm) diameter opening; (4) limit the amount of light attenuation such that the CCD camera is able to view the operation of the spark plug during the combustion ignition process; (5) have an overall small size envelope that satisfies the space limitations of the commercial turbine and combustion test stand; and (6) be capable of many hours of operation without servicing due to the limited and difficult access to its location in the turbine or test stand. Accordingly, there is a long felt need for a combustion camera assembly that satisfies these requirements and improves upon the several limitations found in known designs that have been described above.